Alumina-chromia-phosphorus pentoxide catalyst and method for preparing the same



C L. GUTZElT ET AL ALUMINA-CHROMIA-PHOSPHORUS PENTOXIDE CATALYST Bec. 11, 956

AND METHOD FOR PREPARING THE SAME Filed Sept. 30, 1953 INVENTORS Carlos L- Gutzeit x M//lalm 1% 3H-j BY ATTORNEY 'molecule in the form of methane or ethane.

normally gaseous hydrocarbons.

United States Patent O ALUMlNA-CHROMIA-PHOSPHRUS PENTOXIDE CATALYSI AND METHOD FOR PREPARING THE SAME Carlos L. Gutzeit, Woodbury, and William H. Lang,

Wenonah, N. J., assignors to Socony Mobil Oil Company, Inc., a corporation of New York Application September 30, 1953, Serial No. 383,163

6 Claims. (Cl. 252-437) This invention relates to an improved catalytic reforming process for obtaining gasoline of high octane number. More particularly, the present invention is directed to catalytic reforming carried out in the presence of a catalyst consisting essentially of a cogelled chromiaalumina composite of particularly defined composition impregnated with a specified amount of phosphorous pentoxide and to a process for preparing such catalyst.

Reforming operations, wherein saturated gasoline fractions comprising straight run gasolines, natural gasolines, etc., are treated to improve the anti-knock characteristics thereof, are well known in the petroleum industry. Straight run gasolines generally contain naphthenic hydrocarbons, particularly cyclohexane compounds and parainic hydrocarbons, which are usually of straight chain or slightly branch chain structure, as well as varying proportions of aromatic hydrocarbons. During reforming, a multitude of reactions take place, including isomerization, dehydrogenation, cyclization, etc., to yield a product of increased aromatic content. Thus, in reforming, it is desired to dehydrogenate the naphthenic hydrocarbons to produce aromatics, to cyclize the straight 'chain paranic hydrocarbons to form aromatics, and to effect a controlled type of cracking which is selective both in quality and quantity.

Controlled or selective cracking is highly desirable dur- -ing reforming since such will result in a product of improved anti-knock characteristics.

As a general rule, the lower molecular weight hydrocarbons exhibit a higher octane number, and a gasoline product of lower average molecular weight will usually have a higher octane number. In addition, the isomerization and molecular rearrangement which occurs during reforming also results in products having higher anti-knock characteristics. The splitting or cracking of carbon to carbon linkages must, however, be selective and should be such as not to result in substantial decomposition of normally liquid hydrocarbon into normally gaseous hydrocarbon. The selective cracking desired ordinarily involves removal of one or two lower alkyl groups such as methyl or ethyl from a given Thus, during reforming, it is contemplated that heptane may be converted to hexane, nonane to octane or heptane, etc.

vUncontrolled cracking, on the other hand, would result in decomposition of normally liquid hydrocarbons into For example, nonselective cracking of normal octane would ultimately lead to eight molecules of methane.

Uncontrolled reforming, moreover, generally results in rapid formation and deposition on the catalyst of large vquantities of a carbonaceous material generally referred sity of frequent regeneration by burning the coke there- Y, from. In those instances where the activity of the catalyst ICC is destroyed, it is necessary to shut down the unit, remove the deactivated catalyst, and replace it with new catalyst. Such practice obviously is time-consuming and ineiiicient, imparting a greater overall expense to the reforming operation.

The choice of catalyst for promoting reforming of hydrocarbons to gasolines of enhanced octane rating is dependent on several factors. Such catalyst should desirably be capable of effecting reforming in a controlled and selective manner as discussed above to yield a product of improved anti-knock characteristics. The catalyst selected should, further, be resistant to poisoning and particularly to sulfur poisoning so that sulfur-containing stocks may undergo reforming without the necessity of subjecting the. same to a preliminary treatment for desulfurization. The catalyst should also desirably be characterized by high stability and be capable of easy regeneration, and the method for preparing such catalyst should be commercially attractive, requiring a minimum of equipment and processing stages.

In accordance with the present invention, a catalyst of the above-defined characteristics has been discovered. Broadly, the presen-t invention comprises reforming a naphtha fraction of petroleum in the presence of a catalyst n consisting essentially of cogelled chromia and alumina impregnated with a minor proportion of phosphorous pentoxide. The invention further comprises an improved catalytic composition and a method for preparing the same.

It has heretofore been proposed to employ composites containing the oxides of chromium and aluminum as catalysts for various reactions. Several methods for preparing such catalysts have been proposed, including impregnation of an alumina support with suitable chromium compounds and co-precipitation of solutions containing salts of chromium and aluminum. The diiiiculties encountered in the former method are well known in that a completely homogeneous, active surface is seldom obtained even when tedious methods are used. The latter technique, while overcoming this difficulty, is even more involved and requires extremely close control of pH and other variables to assure satisfactory results. Chromia-alumina composites, heretofore recommended as reforming catalysts, have been found to be characterized by a certain amount of instability, as indicated by the loss of surface area during use. Catalysts of the present invention, consisting essentially of cogelled chromia and alumina impregnated with P205, have been found to have an improved thermal stability, i. e., ability to resist loss of surface area upon aging in comparison with the aforesaid chromiaalumina composites.

The method of reforming naphtha fractions of petroleum in the presence of a cogelled chromia-alumina composite impregnated with P205 as described herein has been found to have certain advantages over the processes commercially available. The advantages obtained upon reforming with the present catalyst, while not fully understood, are believed to result from the method ofk preparation of the catalyst employed. The instant method of catalyst preparation involves the formation of a hydrogel of chromia and alumina preferably containing a chromiaalurnina content of at least lO percent by weight and thereafter impregnating either the washed hydrogel or the dried and/ or tempered material with a solution of a watersoluble phosphate. The acidity of the phosphate impregnating solution should not be such as to detrimentally affect the hydrogel or gel structure. Thus, strongly acid impregnating solutions should be avoided. Mildly acidic impregnating solutions may be tolerated. Preferably, the phosphate impregnating solution is neutral or slightly alkaline. For example, a slightly ammoniacal solution ofl ammonium-phosphate"has been found `to -providef an1 effective impregnating solution. The concentration of the water-soluble phosphate compound in the ,impregnating solution :may `be varied,2 dependingaupon the-'cat-alystfcomposition desired-jl VTh'epliospl1'ateemayf-` be-adde'd by' impregnationofeitherthechromiaialuminaJhydrogel or the dried? orlcalcined chromia-aluminwgeli Sicientfsolution is used so that the particles of chromia-alumina hydrogel' or= gel' maybe completely impregnated; The hydrogel orfgel particles are lpermitted lto remain in Contact withtheimpregnatingirsolution forla predetermined period of time -which is sucientato Apermit l the i solution to -im pregnatethe hydrogel orgel;4V After-completion-ofithe impregnation, the catalyst Yis removedffandslowlyl heated tofanelvated: temperature not ex'ceedingabout` 1000- F. DtrririgthisIheatingitreatrnent, itfis desirable that the atmosph'ere-` surround-ingt the material be free ofi' oxygen. S'ucl-an atmosphere1-is2provided in a preferred embodiment of theeinvenltionl `by lheatingthe impregnated: catalyst int aniatmosphere-lofihydrogens` Thefimpregnated dried catalyst, consistingiessentially off ay cogel ofalumina' and chromia: impregnatedi with` phosphorous 1 pentoxide, is thereafter ready for use.

Composites consisting of a major proportion of alumina, aiminorproportion' of chromia, and a 4minor proportion of phosphorous pentoxide are suitably prepared ".by the methodof'the invention- Catalysts having acomposition of 20 to 40 percent by Weight'of chromia, 50 to180per'cent1by weight-of alumina, and 0.2 toulpercenttby weight. of pho'spliorous'pentoxide are unusuallyetfective for promoting reforming operations-inlwhich a-petroleum naphtha is subjected to conversion to produce a reformed gasoline of improved anti-knock characteristics.' Catalysts having phosphorouspentoxide concentration in the Vrange of 2 tofS` percent Aare particularly. preferred in the. present-inventionf' Thus, af-composite having a composition in the range' off2'5'- to 35- percent chromia,. 60 to 73 percent alumina, andv2 to'S'percentiphosphorouspentoxide, in which chromia and alumina in 1the form of'a ,cogel areimpregnatedfwith phosphorous. pentoxide, represents apre-y ferredernhodiment of the invention.

The"y method of; the invention provides a simplebut highly. effective vprocedure for. preparation .of the. catalyst. Thefcogel of chromia-alumina is `.ai-true, gel yprepared by forming ahydrosol of chromia and alumina, permitting said hydrosol. to lset to-a hydrogel, andfthereafterdrying the'vhydrogel. lf: desired, the hydrogel may be; impregnated'before'drying. T hehydrogel ori-gelfis suitably, but not= necessarily, in particle formv prior toimpregnation. 'lhefparticlesfmay beof irregularsize such as those produced. byfbreakingjup a previously. set dried gel, or the particlesfmay beintheform of extruded or pressed pellets; Preferably,. however, thealurnin'al-chromiav hydrogel or gel particles are in the form ofgspheroidsprepared by introducing'the-hydrosolin the. form vof; globules into a water-immiscib'le medium whereinV thehydrosol globules set tofspheroidal hydrogelV particles. tis particularly preff-.xrred to` prepare. acogelled, catalytic. compositeV of chromia' andi alumina: from a hydrosol havingv an inor.- ganicoXi-de content of atleast about l p ercentby weight inf accordancetwith the= process; described inco-pending application SeriallNo. 201,537, filed December 14, 1950, byfWilliamr-Af. Stover'andfRobiert'C. Wilson, Jr. Such Vprocess .has been set forth-in detail in the aforementioned patent.- Forwconvenience herein, the followingvis offered asia-brief description of saidprocess.

' Attrttechromia-alumina hydrogelhavingametal oxide product concentration of atleast about percent by weight and a relatively` short gelation time, i. e., less than ZhoursA and preferablyv less than 60seconds, is prepared j byzintim'ately adrniXing4 anl organic chromium salt, such as chromicpacetateandan alkali metal aluminate, such as sodium aluminate-toproduce a chromia-alumina hydrosotl.

Tliezihydrosol,sogformedjs-v permitted ,to setv tofa hydrogel. The resulting hydrogel is thereafter subjected to aging lil) andthen. waterfwashed,.dried, and calcined toyield arcata:

It is preferred to` use aqueoussolutions-ofsodiumialuminate and chromium `acetate for preparationY of the abovedescribedhydrogelsr Neither' of" these substancesfis a true chemical compoundz The ratioof `sodium to aluminum can be varied widely as can the ratio of acetate to chromium ion. Variation in the sodium to aluminum ratio of the aluminate solution requires compensating adjustment-of the4 acetatef to chromium. ratio Aofthe second solutionin order! to achievezsatisfactory gelation.y Hydrosols-'lcapablel of set-ting to Vhydrogels in :lessithanaabout-- 20 secondsA arel particularly. desirable forthe` production` of Vbeadlike spheroidal 5 particles z byu methods Wel11:k11o wn 1in thefartgwforrexampl'e, those described'inpatents'to Marisic, suchvasrU S. Patent :No.1 2,384,946; Quick settingzhydrosolsl of lowiv viscosity.v which'. can be; readily handled: at

`beadlfor-rning.nozzles; are thosev prepared from. sodium alurn-ir'iateA solutions.I which; have= a sodium` to aluminum molefratio, referred tof. as z R,1" of? between. 12 and 1.5. Theiacetateltcry chromium mole yratio in the .-chromic acetate solution :employed: should rbenot' less; than 2.8.;R-f1,8 and not more than-4 R;2;4, andipreferably.v in the.l rangez of 41o-2:8 to-4R-24.1

The controlof .the moleratios .discussed ahoveis,readily;1

' Lachieved-Lin therY manufacture of ythe reactant.. solutions.

dichromateawith. glycolic` acid .inf.the. presence ofA acetic l acidas=.describedmorefullyfin U, S. 2,615,0351.

Sodium raluminatez isficonveniently` prepared from-.caustic soda.` of 150? zanmaluminum trihydrate.A Atfazsodium tofaluminum mole ratio yinrthe range 1.25714 to` 1.5/1, .the sodium aluminate is advantageouslymanufactured in an open, .agitated'kettle at 220"F, to v230.or F., withareaction timeof lit/oS-'hours Solutions having alower moleratio downto about; 1.0/ liare. made inran autoclaveat 240F. to`300 E. and'10'to;30 .pounds-.persquare'inch-fgage atrthe samereaction time; Sodium aluminate solutions havinga low sodium.to aluminum ratio of less than 1.3. are relatively unstable andmay be stabilized-by vthe/addition of such organic materials. as. glyceriue, starch, sugar,A and controlled to achieve gelation` at any practicalv solution temperature; Thus, temperatures-from 30' F: to 130 Fi are suitable; Best gelation times have beenexperienced attemperatures between about F; and about 140'='F. The pH of` thechromia-alumina hydrogels is generally between 10`and 13. Forbead formation, a pH' of about 12 hasbeenfound to yield iexcellent results. v

For. thev production of, chromia-alumina hydroagl beads, preparation is carriedv out 'substantially the same -forming in order to Ex the alumina.

-as that described in the above-noted Marisic patent for dividing cone from which a number of small streams ow f into a column of water-immiscible liquid. The temperature of said water-immiscible liquid is desirably maintained ata constant temperature by circulation through a heat exchanger outside the bead forming tower.

The freshly formed chromia-alumina hydrogel abovedescribed is subject to a loss of aluminum as sodium aluminate if inmediately washed with water. This tends to weaken the hydrogel to such an extent that it disintegrates in the wash water. That adverse eect can be avoided by immediately treating the freshly formed hydrogel in fa slightly alkaline aqueous medium. This is generally accomplished by bringing the freshly formed chromia-alumina hydrogel into contact with an aqueous .solution of an ammonium salt of a mineral acid, or a mineral acid, or a mixture of such salt and acid. In a typical operation, the freshly formed hydrogel beads are sluiced out of the forming tower with oil. The hydrogel beads are then separated from the oil and treated with a 20 percent by weight solution of ammonium sulfate. The solution Iis advantageously kept at a pH of 6.0 by the addition of sulfuric acid. It is advisable to maintain a solution of this type in contact with the freshly formed hydrogel for some time after formation. For example, thesolution is re-circulated through the freshly formed hydrogel or otherwise maintained in contact therewith for a period of from about 2 to about 24 hours after Thereafter, the solution may be maintained in contact with the hydrogel for an additional period of about 2 to 24 hours without pH control. During this latter period, the pH of the aging solution may rise from 6.0 to 9.0-9.5. Such treatment of the freshly formed hydrogel is designated herein as aging After aging treatment, the chromia-alumina hydrogel is washed free of anions introduced during aging. The

washed hydrogel can be satisfactorily dried in either superheated steam or air. The hydrogel so dried has been tempered in an atmosphere of hydrogen, nitrogen, carbon dioxide, carbon monoxide, steam, and air. The use of mixtures containing oxygen results in the production of a gel of low mechanical strength. The chromiaalumina gel should, accordingly, be tempered in an inert or reducing atmosphere. y

In accordance with the process of the present invention, it has been found that the heat stability of the chromia-alumina gel catalyst described above for p-romoting reforming is markedly increased by bringing the Vchromia-alumina hydrogel after the alumina content has Vbeen xed by the aforementioned aging procedure into contact with a solution of a phosphorous compound decomposable upon heating into phosphorous pentoxide,

thereafter removing, the hydrogel from said solutionand heating to yield a resultant chromia-alumina gel impregnated with a minor proportion of P205. In general,

the chromia-alumina hydrogel may be brought into contact with the impregnating solution of phosphorous compound at any time subsequent to the above-described aging and washing steps. Thus, the hydrogel, after aging and washing, but before drying,V may be contacted with the impregnating solution and the resultant composite vdried and heated to a temperature suicient to effect decomposition of the phosphorous compound to phosphorous pentoxide, or the dried hydrogel, i. e., gel, may be brought into contact with the impregnating solution and thereafter dried and calcined. Alternatively, the

Acalcined chromia-alumina gel may be impregnated with a soluble phosphate compound and thereafter dried and 'heated to a temperaturesuliicient to convert such phos- 'phare compound to phosphorous pentoxide.

Contact of the chromia-alumina composite with the impregnating solution should, in accordance with the instant invention, be maintained for a suiicient period of time to eiect the deposition of a small amount of phosphorous compound on the surface of the composite. The critical factor in this step is the amount of phosphorous compound incorporated. If either too much or too little phosphorous compound is incorporated, the resulting catalyst does not have the improved characteristics of the catalyst prepared by the method of the invention. Ihe amount of phosphorous compound employed in this step is dependent upon the concentration of phosphorous pentoxide which it is desired to incorporate by impregnation in the nished catalyst and is adjusted by controlling the concentration of phosphorous compound in solution or the amount of the impregnating solution such that when the specied amount of phosphorous compound is incorporated, the ultimate catalyst contains the linal amount of phosphorous pentoxide which it is desired to deposit by impregnation. It has been found that the concentration of phosphorous pentoxide impregnated on the chromia-alumina cogelled catalyst in accordance with the process of the invention should desirably be between about 0.2 and about 10 percent by weight, and preferably between about 2 and about 5 percent by weight of the original catalyst. Amounts smaller than about 0.2 percent P205 have not been found to appreciably increase the thermal stability of the chromia-alumina cogelled catalyst, while large amounts in excess of about 10 percent P205 impregnated on the catalyst surface have been found to unduly increase the extent of coke formation as the catalyst ages.

The chromia-alumina composite, i. e., the aged hydrogel or gel derived therefrom, is thus impregnated with a solution of a soluble phosphorous compound, which compound maybe converted to phosphorous pentoxide by heating. While 4aqueous solutions are to be preferred for practical reasons, other solutions, such as alcoholic solutions or ammoniacal solutions may be used. A concentrated solution Vof just sufficient volume to wet the chromia-alumina composite may be used or a large volurne of a more dilute solution may be used. An important factor in the impregnation of calcined chromia-alumina gel is the presence of soluble chromate ions on the catalyst surface. If a large volume of dilute solution `is used for impregnation, sufficient chromium may be removed from the spent solution to lower the activity of the base catalyst. Accordingly, -it is preferred, when mpregnating the dried or calcined chromia-alumina gel, to subject the same to a preliminary treatment vwith hydrogen to anchor the chromium before such gel is brought into contact with the impregnating solution. Excess solution may be drained from the chromia-alumina composite or it may be evaporated in the presence of such composite to increase the amount of composite impregnated. The impregnation may be carried out under vacuum or under pressure or under a combination of vacuum and pressure. When the composite is a dry gel, it is preferred to evacuate the pores thereof before impregnation in order to avoid shattering of the gel when the same is brought into contact with aqueous .impregnating solution. If,',due to the solubility of the phosphorous compound, it is not possible to incorporate the ,desired -amount of compound in one impregnation, the composite may be dried after the first impregnation and the impregnation repeated until the desired amount of compound is incorporated. While soluble phosphorous compounds capable of conversion to phosphorous pentoxide by heating may generally be used for effecting impregnation, providing the acidity thereof is not such as to adversely aifect the gel structure, it is preferred to employ slightly alkaline compounds of phosphorous. Thus, compounds, such as diammonium hydrogen phosphate, ammonium phosphate, and ammonium dihydrogen phosphate are easily decomposed by heating at moderate temperatures to yield phosphorous pentoxide.

Por/impregnation of thewet'hydrogel', the use of iastrongly acidx impregnatingsolution; should4v beavoidedin order not to injure the catalyst structure. However,- mildly acidic impregnating, solutions, i. et, those having a pH not less than aboutG, may-be usedfor'impregnation of the dried or calcined'chromia-alumnacatalyst:

The impregnation maybe carried out either-as a batch o r' continuous operation; Thus, thev chrornia-alumina' hydrogel, after agingandwashing, maybegpermittedto soak VinY the impregnating solution under` substantially static conditionsl forY the requisite-dime, or the chromia-alumma gel'composite-in the'form of-spheroidalglobules or particlesV of otherdesired`shapefmaybepassed-'through a bath of thel impregnating solution or, alternatively, the impregnating Amedium may be circulatedY through a stationary'bed'ofthe-hydrogelfor gel' particles. Likewise,

' ly, temperatures somewhatf above the minimum decomposition temperature are preferred. On the other hand, veryA high temperatures cause sintering andA are to` be avoided. The rateof heating should be comparatively slow, generally not ineXcess-of "F, per minute. Where spheroidal particles are being treated,` the rate of'heating should ordinarily not exceed'about 4 F.' per minute. Temperatures in the range of 300 F. to 1000o F; are quite suitable in nearly all cases, but' somewhat lower temperaturesmay'be applied in somecases and higher tempcraturesup t-o about 1400 F. may be employed ifdesired Duringv thisy heating treatment, it is desirable that ther atmosphere surrounding the composite be free (3f-oxygen; It is. particularly feasible, although not essential, to ush thechromia-alumina composite with a'fred'ucing -gasjsuch as hydrogen during the calcination to -avoid chromate formation during the initialheat'treatment. This is especially desired for composites, the structure ofv which has not been setby previous calcination, such as hydrogels in the-wet or dry state; The calcination is usually continued'until' the impregnated phosphorous compound is completely rdecomposed but is dis- Example 1 A A chromiafalumina hydrogel; was.- prepared-,1: fromk the following reactants.;

Solution A.-?Diluted sodiumaluminatef containingi approximately 18.3` percent A1203,y 14.4.percentNa2O, and 67.3' percentI-IZOr Solution. B.Diluted chromieacetate; preparedby.y reduction of sodiumchromatevwith glycoliccacid and containingl approximately. 26.0` percent;l (li-.(.GHaGQOJa 1.4

percent oroma, 21s percent crncooNa, 555 percent (COGNa'h, 0.6l percent HCQONa, 0.8 percent CHzOHCOONa and 63.4'percentH`2O.

SolutionsA and` B were pumpedseparatelyunder pressure to .an eiicient mixing nozzle. The solutions were heated to:125 F. and mixed. in equal volumesVv at a -rate of 1.06. gallons per minute. The resulting stream of hydrosolowed. overa divider into a columnof! oil. The hydrosol set to beadsof hydrogel and the resulting hydrogel beads were sluiced from the bottom ofthe forming tower. in a'stream of oil;4 After. separating oil from thehydrogelbeads, thelatter were aged in.a=20 percent by weight aqueous solutionof ammonium` sulfate. Since the pH of the aging-solution-,rises as it ows through the fresh hydrogel beads, sulfuric acid was: added in sufficient amount to maintain a pH of about.1610. The

bead. hydrogel was: aged in thissolution for 24- hours, after which itwas allowed to age-an additional Sfhours l without pH control. During this latter period, the'pH ofthe aging solution'rose frornabout. 6;-0 to about4 9.15. After aging, thehydrogel was washeduntil'a sulfate-free washwater was indicated. Theawashedhydrogel hadla product. concentration of 18.3 percent by` weight. The hydrogel was thereafter driedi in 100 percent" steamat 230-2359 F. for 7: hours, then gradually raised toA 350 F. over a periodr of about 2 hours, and then tempered by heating inaclosed vessel to 11'00" F. at the'rateof 2.1/2.o F. per minute.r TheY resulting beads of gel contained24 mole percentCrzOsand 76 mole percent A1203. This catalyst is representative of thaty produced by the aforementioned'. processof Stover and Wilson: and may be considered as a blank forl comparison, with the catalysts whichl have undergoneJ treatmentA in accordance with the present process.

Example 2 A chromia-aluminahydrogel, prepared asin Example 1, was treated, after aging and washing, with an aqueous solution containingenough diammoniumhydrogen phosphate so that the phosphate ions, upon complete absorption, produced 1.5 percent by weight P205 after calcination. After allowing the hydrogel tosoak for about 16 hours, the hydrogel particles were'rernoved, drainedand washed slightly to remove adhering.A solution. Analyses of the drained liquid showed substantially. complete removal'of Vthe phosphate ions and norextraction of chromium. The wet impregnated particles were dried at 175 F. in aclosed vessel, thereby providing a water-saturated atmosphere during the early drying stage and preserving a maximum proportion of whole gel particles. The partially dry particles rwere then heated to l000 F. ina rhydrogen atmosphere over` a'4-hour period and then maintained at 1000'F. inhydrogen for 12 hours.

Example 3 The chromia-alumna hydrogelof Example 1 wasimpregnated with 2.0 percent P205 by the procedurev ofEX- ample'Z;

Example 4 The chromia-alumina'hydrogel of Example 1 was-:impregnated with 3.0 percent-P205. by the;procedure. ofExample 2..

Example 5.

The chromia-alumina hydrogel of Example 1"was mpregnatedwith 510 percent- PaO's by the procedure offEX- ample 2.

Example f 6" A' chromia-.alumina gel, prepared asin Example` 1, was treated'after aging, washing, drying, and calciningwith an' aqueous solution of diammoniumhydrogen phosphate dissolve'd'injust enough water to completely cover. the gel particlesf and to form 0l6percent by weight 17203Y upon ignition. After allowing to stand 16 hours, the impregnated gel particles were drained and dried in air about 16 hours at about 180 F. and then calcined in a hydrogen atmosphere at 1000 F. for 12 hours.

Example 7 Chromia-alumina gel particles, prepared as in Example 1, were -impregnated with 1.9 percent P205 by the procedure of Example 6.

Example 8 Chromia-alumina gel particles, prepared as in Example 1, were impregnated with 3.1 percent P205 by the procedure of Example 6.

Example 9 A chromia-alumina gel, prepared as in Example 1, was treated, after aging, washing, drying, and calcining, with hydrogen for 12 hours to ix the chromium. The reduced calcined chromia-alumina gel was then brought into contact with an ammoniacal solution containing sufficient ammonium phosphate to form 2.5 percent by weight P205 upon ignition. After allowing to stand 16 hours, the impregnated gel particles were dried 12 hours in air at 180 F. and then heated to 1000 F. in a hydrogen atmosphere over a 4-hour period and calcined at 1000 F. in hydrogen for 12 hours.

Example 10 A chromia-alumina gel, prepared as in Example 1, was treated and impregnated with 6.2 percent P205 by the procedure of Example 9.

Example 11 A chromia-alumina gel, prepared as in Example 1, was` treated and impregnated with 12.4 percent P205 by the procedure of Example 9.

The foregoing catalysts were tested for stability under thermal conditions encountered in the reforming of petroleum naphthas. The data obtained upon testing are shown graphically by the attached curves wherein:

Figure l represents the change in surface area, in square meters per gram, of the untreated and treated chromia-alumina catalyst impregnated with varying amounts of P205 in the hydrogel state.

Figure 2 represents the change in surface area, in square meters per gram, of the untreated and treated chromiaalumina catalyst impregnated with varying amounts of P205 after the gel has been dried and calcined.

Figure 1 shows that, when the chromia-alumina gel particles are impregnated before drying, there is an increase in the initial surface area after calcination in hydrogen with an increase in the phosphate content up to percent P205. There is a parallel increase in surface area stability with phosphate content for heat treatment in air at 1300 F. or 1400 F. At higher calcination temperatures, the surface area stability drops oi rapidly for all these catalysts. If the gel particles are impregnated after calcination as shown by the data of Figure 2, appreciable phosphate addition results -in reduced initial surface area. This decrease in surface area is apparent for the chrornia-alumina gel impregnated with 12.4 weight percent P205. For relatively high phosphate concentrations, an increase in surface area stability with increasing phosphate concentrations is shown even after heat treatment at 1560 F. The results of Figures 1 and 2 show that the heat stability of the catalyst increased with increasing concentrations of P205 impregnated on chromiaalumina gel particles.

The present catalyst, comprising a major proportion of alumina and a minor proportion of chromia in the form of a cogel impregnated with phosphorous pentoxide generally possesses improved thermal stability over a chromiaalumina composite of corresponding composition which has not undergone impregnation with phosphorous pentoxide. It would accordingly appear that the advantages achieved with the treated catalyst of the invention are 'ous pentoxide when the same are deposited -on a chromiaalumina gel prepared as described herein.

What is claimed is: v

1. A catalytic composite consisting essentially of 20 to 40 percent by weight of chromia, 50 to 80 percent by weight alumina, and 0.2 to 10 percent by weight of phosphorous pentoxide, wherein the chromia yand valumina components in the form lof a cogel are impregnated with the phosphorous pentoxide component.

2. A catalytic composite consisting essentially of 25 to 35 percent by weight of chromia, 60 to 73 percent by weight alumina, and 2 to 5 percent by weight of phosphorous pentoxide, wherein the chromia and alumina components in the form of a cogel are impregnated with the phosphorous pentoxide component.

3. A method for preparing an intimate catalytic` composite of chromia, alumina, and phosphorous pentoxide, which .comprises forming a chromia-alumina cogel consisting of a major proportion of alumina and a minor proportion of chromia, calcining said chromia-alumina gel, reducing safid calcined chromia-alumina gel with hydrogen, bringing said reduced gel into contact with an aqueous solution of a water-soluble phosphorous compound, maintaining said contact for a predetermined time suicient to eiect impregnation of said gel with said solution, removing the gel from the impregnating solution, and drying the same to yield a chromia-alumina gel containing 20 to 40 percent by weight of chromia, 50 to 80 percent by weight of alumina and impregnated with between about 0.2 and about 10 percent by weight of phosphorous pentoxide, and thereafter slowly heating the resulting gel product in a hydrogen atmosphere to an elevated temperature not exceeding about 1000 F. at a rate not in excess of 10 F. per minute.

4. A method for preparing an intimate catalytic composite of chromia, alumina, and phosphorous pentoxide, which comprises preparing a chromia-alumina cogel consisting of a maj-or proportion of alumina and a minor proportion of chromia by mixing aqueous solutions of sodium aluminate and chromic acetate to yield a hydrosol having a chromia-alumina content of at least about 10 percent by weight, controlling the sodium to aluminum ion ratio and the acetate to chromium ion ratio in said solutions to effect rapid gelation of said hydrosol to a hydrogel, aging the hydrogel so obtained, Washing the aged hydrogel, drying and tempering the same to yield a resulting hard chromia-alumina gel, reducing said gel with hydrogen, bringing the reduced gel into contact with an vaqueous solution of a water-soluble phosphorous compound, and main-taining said contact for a predetermined time suicient to eect impregnation of said gel with said solution, removing the gel from the impregnating solution, and drying and calcining the same in an oxygen-free atmosphere to yield a chromia-alumina gel containing 20 to 40 percent by weight of chromia, 50 to 80 percent by weight of alumina and impregnated with a small amount in the range `of 0.2 to l0 percent by weight of phosphorous pentoxide.

5. A method for producing an intimate catalytic composite of chromia, alumina, and phosphorous pentoxide, which comprises preparing a chromia-alumina cogel by mixing aqueous solutions of sodium alurninate and chromic acetate to yield a hydrosol having a chromiaalunrina content of at least about 10 percent by weight, controlling the sodium to aluminum ion ratio and the acetate to chromium ion ratio in said solutions to eiect rapid gelation of said hydrosol to a hydrogel, aging the hydrogel so obtained, Washing the aged hydrogel, bringing the washed hydrogel into contact with an aqueous solution of a water-soluble phosphorous compound and maintaining said contact for a predetermined time suiicient to effect impregnation of said hydrogel with said solution, removing the hydrogel from the impregnating solution, and drying the same to yield a chromia-alumina gel containing 20 to 40 percent by weight of chromia, 50 to 80 percent "11 by-fvveigh't'ofL aluminaand impregnatedawith between'l 01:2 and' lOlpercent by WeightA of, phosphorous pentoxide, and thereafter slowly Vheatiufgfthe resulting ygelproduct' in a.' hydrogen atmosphere to an elevatedf temperatur'etnot'f eX- ceeding about 1000'J F. at a rate not in-.excessof 10 F. per minute.

6. A'- lmethod for producing .anintimate catalyticr compositel ofl ohroniia, valumina and phosphorous pentoxide, which comprises"forming'spheroidal particles of chromiaalumina gel, caleining the gel' particles,v reducing the calcined gel particles with hydrogen, bringing the reduced particles into Contact with an aqueousl ammonium phosphate solution, maintaining said contacti forL a. predetermined time sutlcient to' effect impregnationv of: said particles with said f s'o1ution5 removing' the particlesf from the impregnating solution, and dryingY the.r same toV yield spheroidal' particles of ohrornaaalur'niijav gely containingrZS hydrogen atmosphere to an elevated temperature not ex` c'eedng aboutg 1000"' F. at a rate not in excess 'ofabout 49T.' perminute.

References CtedYin-therle of this patent UNITED. STATES PIVYTENTSA 2';l7:1,207 Boultbee Aug. 29, 1939 2,440,236 Stirton Apr. 27`, 1948 2,635,082

Smith Apr. 14, 1953 

1. A CATALYTIC COMPOSITE CONSISTING ESSENTIALLY OF 20 TO 40 PERCENT BY WEIGHT OF CHROMIA, 50 TO 80 PERCENT BY WEIGHT ALUMINA, AND 0.2 TO 10 PERCENT BY WEIGHT OF PHOSPHOROUS PENTOXIDE, WHEREIN THE CHROMIA AND ALUMINA COM- 